ideal camshaft for road xflow

[eric]

my 1600 SPRINT CATERHAM is fitted with a stage 2 Head

and 2 Webers 40 and an A2 cam.

My question is very simple: for you what is the best cam for road

 

Many thanks for all

[Petrolhead]

Can't remember exactly but my xflow used a kent 244 which was nice and tractable. I almost thought that I could have got away with the 254. Have tried to locate their web site with no luck.

 

Better to go in a blaze of glory than to fade away teeth.gif

[oilyhands]

Your A2 is an old cosworth profile and has relatively low lift, the 234 profile is equivalent but has slightly less overlap, the 244 is quite a bit hotter, but if properly setup in a light car like a seven it shouldnt give too many problems, you will need to pocket the pistons for either the 234 or 244, the 254 is probably a bit too hot for everday road use unless you like your engine peaky. FWIW

 

cam lift dur inlet exhaust clearances

A2 .349" 286 35/71 71/35 .020 .022

BCF2 .382" 290 37/73 73/37 .014 .018

234 .423" 280 37/63 73/27 .022 .024

244 .447" 290 42/68 78/32 .022 .024

254 .470" 300 47/73 83/37 .022 .024

 

The 2(x)4 range are all asymetric with both lobe centres advanced over the older profiles.

 

Oily

[kenny.]

Totally agree with lads on the 244 suggestion...my last x/flow car (1690cc/711m block) used this with BVH and 45's.Car was totally driveable on road and had a lovely power band on track. Only other points I'd comment on were insurance bits fitted as well....ie duplex chain, h/p pump and steel posts etc. Sprint may already have these, but with this set-up mine was quick, bullet proof and hassle free.

 

Keny HPC

 

 

[Big Brother]

Oilyhands,

If an engine has been built with a 234 cam and pocketed pistons and is upgraded by fitting a 244, will the pockets in the pistons need to be enlarged/deepened?

 

 

Also do you know the correct spec for valve springs on a Supersprint with a 234 cam.

 

Just Curious

 

Steve

 

cool.gifScream...if you want to go faster!!!id=limegreen> cool.gif

[Big Brother]

Petrolhead,

 

Kent Cams

[oilyhands]

If the pistons have been pocketed correctly (pockets increased by .100") then they should be OK with the 244 and 254.

 

The recommended springs for the 234 are the Kent VS6 doubles at an installed height of 31.97mm. These are 260lb ones I think.

 

Oily

[hubcap]

What cam does the 1700 x-flow have as supplied by Caterham in supersprint spec, I was led to believe that it was a Kent 234, is this correct? If so would a move to a 244 cam be beneficial, especially on the track, rather than the road (given the valves remaining as supersprint size), or would a fair amount of head work be needed before the cam upgrade became worthwhile?

 

Hubcap

[eric]

Hi

 

I can confirm that the 1700 supersprint cam is the 234.

 

 

[oilyhands]

Properly setup an upgrade to 244 would give a useful boost, but the recommended valve springs and installed height of same are different since the 244 has greater lift. If this isn't seen to by machining the valve spring seats correctly you could end up coilbound with all its resultant nasties.

 

I've no doubt that the engine could benefit from some more head work and maybe re-calibration of the carbs.

 

Oily

 

Edited by - oilyhands on 16 Sep 2001 18:36:22

[Big Brother]

Thanks Oily

 

 

Steve

 

cool.gifScream...if you want to go faster!!!id=limegreen> cool.gif

[Roger King]

The A2 cam is a 1960s Cosworth profile and was used by Caterham in the 'Sprint' engine. The 234 is the Supersprint cam and is a more modern profile in line with the high lift, short duration philosophy. This is almost the complete opposite of the way the A2 was designed. The down side of high lift, short duration is that the valve gear suffers and must be upgraded to suit.

 

The 234 will give a considerable power boost over the A2 if all else is equal, but without any real loss of driveability. The 244 is near as dammit as good as the 234 for driveability, but again has better top end power. Even the 264 can be driven happily round a car park if set up properly, but you won't have much power below 4500rpm.

 

However, fitting a cam is not a job to be done in isolation. The rest of the valve gear will need uprating (especially the valve springs) and the rest of the engine must be upgraded to suit. In particular you may need to use forged pistons because the standard item is simply not up to the job; certainly not if a 244 is used. Premature piston ring failure and even broken pistons are very common when used with the more exotic cams unless the forgings are fitted.

 

When upgrading an engine you need to look at it as a package of measures rather than individual items that will each give a power boost. I can illustrate this with the example we once saw of an engine that was pretty much standard except for a full race cam. The cam wouldn't let engine produce any meaningful power at low revs and just where the cam would have started to work, the valves, porting, carbs, etc refused to breathe properly resulting in poor top end as well. Result was an engine that didn't go well at any revs and was in fact slower than a completely standard engine.

 

Personally, I would advise a 234 as an excellent road cam if you don't want to go too far with the rest of the engine.

[SteveP]

Just to echo what has already been said. I have a Superprint with 244 cam and on 45DOCEs plus the other upgraded bits (duplex timing chain, steel rocker posts, double valve springs, etc) and it's great on the road - lots of grunt, plenty fast enough and so-far reliable. Not had it on the circuit yet though.

 

Also, a follow up question from a point mentioned by Roger King. Not had the car that long but when I spoke to the engine builder he mentioned that forged pistons had been originally fitted - great. Having looked at the history, noticed that the pistons have been replaced (last year, by Arrowstar Racing) but it doesn't mention what for. They cost about £30 each. Being a total novice - am I safe to assume at this price that they are forged pistons? Or likely to be standard cast items?

 

I don't really want one snapping or failing on me. Could check with Arrowstar, but thought I'd try you guys first.

 

Thanks

Steve P

[oilyhands]

Forged pistons would be more like £80-100 a pop , I would question Arrowstar carefully.. £30 seems very inexpensive, maybe it was just the rings that were replaced.

 

Oily

[greg]

Any here any thoughts on the 254 as a fast road cam (given other sensible mods) or is the 244 the best comprimise ?

 

Greg, Q 880 RAE (Green/Ali XF)

[SteveP]

OK, now I'm worried. I will be questioning Arrowstar but assuming that they have just put bog standard pistons back in (which seems likely now), what exactly are the chances of something catastrophic happening to my engine? Roger said it was very common for the piston rings and even the pistons to fail with a 244 cam.

 

At the moment I run it reasonably quickly up to about 6k revs.

 

I'm looking to do a fair bit of hillclimbing / sprinting next year and don't really want a piston breaking on me.

 

For those others who have / had a xflow with this cam, did you also have forged pistons?

 

Should I be shelling out £350+ and machining costs to put my mind at rest?

 

Slightly panic-ing!

Steve P

[Petrolhead]

Thanks Steve.

 

Just for a info, and I know Roger you have commented on this before, my Xflow user twin can flat top pistons which has the tops saved a litle to get a reasonable compression ration. Due to the cost (Low back in 1992) compared to forged they were an excellend compramise being durable and a lot lighted than the std Xflow pistions which are on the heavy side and tend to break if over revved. These pistons, Kent 244, Duplex, steel rockers, Vulcan (Are they still around??) Large Valve head and fully ballanced gave a sweet, tractable engine that gave 20000 reliable use.

[Roger King]

Steve,

 

I assume that your engine is 1700ccm? If it is this leads to a puzzle with your pistons because the standard piston (Supersprint) runs a bore of approximately 83.25mm wherea the forgings are at 83.5mm. In other words, they are not interchangeable and I really don't know what is going on with your engine.

 

It is of course possible that your original forgings were specially made, but it seems unlikely. Forged pistons are approx £100 each depending on exact spec.

 

Greg,

 

254 is perfectly usable on the road in a light car such as a 7, so long as you are happy to have all the action at higher revs. This does not mean that the engine will not run quite happily at lower revs (when set up properly), just that it won't have lots of power low down. Several of our customers run this cam and are very happy with it once we have made them aware of it's characteristics. It is however, very demanding on your valve gear and other components, so don't do it unless you are prepared to do the whole engine properly.

[greg]

Thanks Roger,

 

I'm not that fussed below 3K rpm - as long as it pulls ok. My present setup with a Piper 285 has an excellent flat torque curve, which is very good, yet a bit borring. My valve gear is apparently uprated (dual ikensian spings and duplex chain ?!?)

 

Greg, Q 880 RAE (Green/Ali XF)

[Casbar]

I've just bought a 244 Kent cam, and have a 234 fitted at present. According to the info in the cam kit, the springs and height are the same as for the 234. Although there are new springs in the kit.

 

Robert

[oilyhands]

According to the info I have the 244 has another 25 thou of lift and with the recommended 234 springs would go coilbound, unless they are using different springs than those I have listed then your existing springs could well be unsuitable, use the ones that have come with the 244 kit and make sure the installed height is as per the instructions.

 

Oily

[Casbar]

I'm going to use the springs that came with the 244 kit. But I also checked on the Kent cams web site and there is a dif in lift. So I rang the Kent tech department, the guy there told me that the 234 springs and the 244 springs are the same part number. And if the head had already been machined for a 234, then as long as the piston pockets are ok, no more work will be required on the head. Just put the new springs in and check the piston clearence

 

Robert

[SteveP]

Thanks Roger for your help.

 

Yes it is a 1700.

 

I've since contacted Arrowstar who unfortunately couldn't tell me what pistons they had fitted (hmm) although I was quoted £87 +VAT each for a forged one. Perhaps Oily was right is saying that only piston rings were fitted - do piston ring sets really cost £30 per piston? (You can see how new I am to this).

Still awaiting a call back from someone at Arrowstar who supposedly knows what has happened.

 

Wasn't aware of the difference in bore size between std and forged and therefore now trying to check with original engine builder to verify that forged were definitely fitted at the outset.

 

Apart from partial stripping of the engine, I don't suppose there is any easy way to tell what's been fitted, is there?

 

Other people have said that forged pistons make a distinctive sound, like a big end rattle but I can't say that I've noticed any such noise.

 

Cheers

Steve P

[oilyhands]

Casbar,

 

They may well use the same springs now, but only a short while ago they listed and supplied different springs for the 234 (VS6) and 244 (VS7), these had different installed heights and therefore different maximum lift before going coil-bound. I'd be unsure as to which springs were fitted to your current 234, if it was fitted a few years ago there is a good chance you have the older springs and installed height. To be sure measure the installed height, if it is 32mm or so then you have the older springs and the platforms will need machining by 2mm, if the installed height is 34mm or so then you have the later common springs.

 

Stevep,

 

Rings vary in price according to application, £30 is a little steep for rings, £15-20 per piston is closer, my comment was a guess which I thought might jog your memory. £30 is certainly closer to the price of a ring set than a forged piston. Depressingly it's also a reasonable price for a cast piston.

 

Oily

[Roger King]

The VS6 spring for the 234 cam was discontinued several years ago, possibly as many as 8 years ago. It was quite useful because it would normally fit on an unmodified head and give approximately the correct installed height. The VS7 which is now recommended, requires considerable valve spring platform machining to achieve the correct height.

 

The upside to this is that the VS7 is a much better spring. Back in the days of Class B Crossflow racing in the Caterham series, we found that the VS6 springs would break if revved to 7000rpm. In fact we never used them on a race engine because we were using up to 8000rpm, but some others did with consequent failures.

 

I have never seen a Supersprint with anything other than VS6 springs fitted, so either Caterham had a lot of stock or they have been using something that looks the same.

 

Regarding the knocking noise with forged pistons. I have only come across this with Arias pistons. These are from California and are made of a different alloy to that used by most European manufacturers. They expand rather more when hot, so have to run a bigger bore clearance and even more importantly they have a different skirt profile which lets the piston rock at end of it's stroke. Most forgings are every bit as quiet as the standard piston.